In MATLAB, you cannot access the previous iteration of a loop directly. If you want to utilize that information you need to either index your results, or record the previous iteration as a separate variable.
% Index method
i = 0;
while true
i = i + 1;
y_pred(i) = ...
if abs(y_pred(i)-y_corr) < e
break
end
y_corr = y_pred(i);
end
% Variable method
while true
i = i + 1;
y_pred = ...
if abs(y_pred-y_corr) < e
break
end
y_prev = y_corr;
y_corr = y_pred;
end
